This question is more for Catholics I suppose. The Lord's Prayer is a prayer that should be prayed daily i.e. "Give us this day our daily bread". Why do Catholics have to go to regular confession to have their sins forgiven if they pray The Lord's Prayer and ask for forgiveness daily i.e. "Forgive us our trespasses as we forgive those etc?
The Church teaches by Canon Law that a penitent must go to confession for mortal sins (see 1 Jn 5:16-17). I have also included the prior canon providing an explanation of the proper disposition and intention of the pentitent.
Canon 959 In the sacrament of penance the faithful who confess their sins to a lawful minister, are sorry for those sins and have a purpose of amendment, receive from God, through the absolution given by that minister, forgiveness of sins they have committed after baptism, and at the same time they are reconciled with the Church, which by sinning they wounded.
Canon 960 Individual and integral confession and absolution constitute the sole ordinary means by which a member of the faithful who is conscious of grave sin is reconciled with God and with the Church. Physical or moral impossibility alone excuses from such confession, in which case reconciliation may be attained by other means also.